IP routing optimization in an access network

ABSTRACT

In an access network which supports a mobile IP protocol, a mobile station may perform several handovers between access nodes during a long session which may cause inefficient mobile IP routing. In the present invention, an access node, which is the target of a handover during an IP session, is arranged to check the preferred mobility agent in respect of the optimal routing on the mobile IP level, and if a more preferred mobility agent is available and not the same as a current mobility agent, the connection to the current mobility agent is closed, and a new connection to the preferred mobility agent of the respective access node is opened. In merit of the new connection established by the access node to the preferred mobility agent, the agent advertisement messages sent by the new mobility agent can be received by the mobile node, and thereby the mobile node is able to detect the change of the attachment point (i.e. mobility agent) and to initiate standard mobile IP registration.

RELATED APPLICATIONS

[0001] This is a continuation application of the international patentapplication PCT/FI00178, filed on Mar. 8, 2000.

FIELD OF THE INVENTION

[0002] The invention relates to a mechanism for optimizing the routingof macro level traffic, such as Internet-type protocol traffic, in anaccess network, such as a radio access network.

BACKGROUND OF THE INVENTION

[0003] Mobile communications system refers generally to anytelecommunications system which enable wireless communication when usersare moving within the service area of the system. A typical mobilecommunications system is a Public Land Mobile Network (PLMN). Often themobile communications network is an access network providing a user withwireless access to external networks, hosts, or services offered byspecific service providers.

[0004] The general packet radio service GPRS is a new service in the GSMsystem (Global System for Mobile communication). A subnetwork comprisesa number of packet data service nodes SN, which in this application willbe referred to as serving GPRS support nodes SGSN. Each SGSN isconnected to the GSM mobile communication network (typically to a basestation controller BSC or a base station BTS in a base station system)so that the SGSN can provide a packet service for mobile data terminalsvia several base stations, i.e. cells. The intermediate mobilecommunication network provides radio access and packet-switched datatransmission between the SGSN and mobile data terminals. Differentsubnetworks are in turn connected to an external data network, e.g. to apublic switched data network PSPDN, via GPRS gateway support nodes GGSN.The GPRS service thus allows to provide packet data transmission betweenmobile data terminals and external data networks when the GSM networkfunctions as a radio access network RAN.

[0005] Third generation mobile systems, such as Universal MobileCommunications system (UMTS) and Future Public Land MobileTelecommunications system (FPLMTS), later renamed as IMT-2000(International Mobile Telecommunication 2000), are being developed. Inthe UMTS architecture a UMTS terrestrial radio access network, UTRAN,consists of a set of radio access networks RAN (also called radionetwork subsystem RNS) connected to the core network (CN). Each RAN isresponsible for the resources of its set of cells. For each connectionbetween a mobile station MS and the UTRAN, one RAN is a serving RAN. ARAN consists of a radio network controller RNC and a multiplicity ofbase stations BS. One core network which will use the UMTS radio accessnetwork is the GPRS.

[0006] One of the main targets in the development of mobilecommunication networks is to provide an IP (Internet Protocol) servicewith a standard IP backbone which would use a combination of differenttypes of mobile network mobility managements in the mobile networks andMobile IP. The basic IP concept does not support the mobility of theuser: the IP addresses are assigned to network interfaces in dependenceon their physical location. In fact, the first field of an IP address(the NETID) is common to all interfaces that are linked to the sameInternet subnet. This scheme prevents the user (the mobile host) fromkeeping its address while moving over different Internet subnets, i.e.while changing the physical interface.

[0007] In order to enhance the mobility in the Internet, a Mobile IPprotocol for IP version 4 have been introduced by the InternetEngineering Task Force (IETF) in the standard RFC2002. Mobile IP enablesthe routing of IP datagrams to mobile hosts, independently of the pointof attachment in the subnetwork. The mobile IP protocol introduces thefollowing new functional or architectural entities.

[0008] ‘Mobile Node MN’ (also called Mobile Host MH) refers to a hostthat changes its point of attachment from one network or subnetwork toanother. A mobile node may change its location without changing its IPaddress; it may continue to communicate with other Internet nodes at anylocation using its (constant) IP address. ‘Mobile Station (MS)’ is amobile node having a radio interface to the network. A ‘Tunnel’ is thepath followed by a datagram when it is encapsulated. In this model adatagram, while encapsulated, is routed to a known decapsulation agent,which decapsulates the datagram and then correctly delivers it to itsultimate destination. Each mobile node is connected to a home agent overa unique tunnel, identified by a tunnel identifier which is unique to agiven Foreign Agent/Home Agent pair.

[0009] ‘Home Network’ is the IP network to which a user logicallybelongs. Physically, it can be e.g. a local area network (LAN) connectedvia a router to the Internet. ‘Home Address’ is an address that isassigned to a mobile node for an extended period of time. It may remainunchanged regardless of where the MN is attached to the Internet.Alternatively, it could be assigned from a pool of addresses.

[0010] ‘Mobility Agent’ is either a home agent or a foreign agent. ‘HomeAgent HA’ is a routing entity in a mobile node's home network whichtunnels packets for delivery to the mobile node when it is away fromhome, and maintains current location information for the mobile node. Ittunnels datagrams for delivery to, and, optionally, detunnels datagramsfrom, a mobile node when the mobile node is away from home. ‘ForeignAgent FA’ refers to a routing entity in a mobile node's visited networkwhich provides routing services for the mobile node while registered,thus allowing the mobile node to utilise its home network address. Theforeign agent detunnels and delivers packets to the mobile node thatwere tunnelled by the mobile node's home agent. For datagrams sent by amobile node, the foreign agent may serve as a default router forregistered mobile nodes.

[0011] RFC2002 defines ‘Care-of Address’ (COA) as the termination pointof a tunnel toward a mobile node for datagrams forwarded to the mobilenode while it is away from home. The protocol can use two differenttypes of care-of address: a “foreign agent care-of address” is anaddress announced by a foreign agent with which the mobile node isregistered, and a “co-located care-of address” is an externally obtainedlocal address which the mobile node has acquired in the network. An MNmay have several COAs at the same time. An MN's COA is registered withits HA. The list of COAs is updated when the mobile node receivesadvertisements from foreign agents. If an advertisement expires, itsentry or entries should be deleted from the list. One foreign agent canprovide more than one COA in its advertisements. ‘Mobility Binding’ isthe association of a home address with a care-of address, along with theremaining lifetime of that association. An MN registers its COA with itsHA by sending a Registration Request. The HA replies with a RegistrationReply and retains a binding for the MN.

[0012] A single generic mobility handling mechanism that allows roamingbetween all types of access networks would allow the user toconveniently move between fixed and mobile networks, between public andprivate networks as well as between PLMN's with different accesstechnologies. Therefore, mechanisms supporting the Mobile IPfunctionality are also being developed in mobile communication systems,such as UMTS and GPRS.

[0013] It is desired that the Mobile IP be implemented as an overlay ofthe UMTS/GPRS network while maintaining backwards compatibility withpresent systems, assuming minimal modifications in the GPRS standardsand in networks whose operators do not want to support the MIP. FIG. 1illustrates the minimum configuration for a GPRS operator who wishes tooffer the mobile IP service. The current GPRS structure is maintained,i.e. the GPRS handles the mobility within the PLMN, while the MIP allowsthe user to roam between other systems, such as LAN's, and UMTS withoutloosing an ongoing session. In FIG. 1 the foreign agents FA are locatedat GGSNs. All GGSNs may not have FAs. The SGSN and the GGSN may also beco-located. One FA in a PLMN is sufficient for offering the MIP service,but for capacity and efficiency reasons, more than one may berecommendable. This means that the MS must request a PDP context to beset up with a GGSN that offers FA functionality. While setting up thePDP context, the MS is informed about network parameters of the FA, e.g.care-of address.

[0014] The MS may have the same care-of address COA during a session,i.e. as long as a PDP context is activated. A very mobile MS mightperform several inter-SGSN HOs during a long session which may causeinefficient routing. As an initial improvement, a streamliningprocedure, with a temporary anchoring point in the GGSN, could beintroduced: If the MN is not transferring data, or is possibly even inthe active state while moving from one SGSN to another, a new PDPcontext could be setup between the new SGSN and its associated GGSN atthe handover. The MN will receive a new care-of address. If the MN weretransferring data, e.g. were involved in a TCP session, the MN wouldmove from the old SGSN to the new one while keeping the PDP Context inthe old (anchor) GGSN for the duration of the data transfer. Once thedata transfer is terminated, the PDP Context can be moved to the GGSNassociated with the new SGSN and a new care-of address can be obtained.

[0015] The problem is how to discover the movement and to find a newforeign agent FA, preferably the nearest one, when the MN is moving fromone SGSN to another. The GPRS terminal (MS) is naturally aware of thechange of the SGSN on the GPRS protocol level as described above butthis change is transparent to the overlaying MIP protocol and the mobilenode MN associated with the GPRS terminal MS.

[0016] Similar problems may be encountered in any mobility managementand routing on a system level overlaying the mobility management of anaccess network. These various overlaying mobility managements arecommonly referred to as macro mobility management herein.

DISCLOSURE OF THE INVENTION

[0017] An object of the present invention is to overcome or alleviatethe above described problems.

[0018] The object is achieved by a method, a system and an access nodewhich are characterized by what is disclosed in the attached independentclaims. Preferred embodiments of the invention are disclosed in theattached dependent claims.

[0019] In the present invention a support node, or more generally anyaccess node, which is the target of a handover during a session, isarranged to check the optimal routing in respect of macro mobilitymanagement, too. For that purpose, the access node is aware of the mostpreferred mobility entity, normally the closest one, which should beused. A mobility entity may be any entity which provides a point ofattachment on the macro mobility level, such as a mobility agent in themobile IP-type mobility management. In a handover situation the system,preferably the access node, checks whether there is a more preferredmobility entity which should substitute for the current mobility entityof the session. If there is no preferred mobility entity for that accessnode, or the preferred mobility entity appears to be the same as thecurrent mobility entity of the session, the current mobility entity ismaintained. However, if there is a more preferred mobility entity forthat access node and the preferred mobility entity is not the same asthe current mobility entity, the connection (e.g. a PDP context) to thecurrent mobility entity is preferably closed (released), and a newconnection (e.g. PDP context) to the preferred mobility entity of therespective access node is opened. Registration in accordance with thespecific macro mobility management scheme can be carried out.

[0020] In the preferred embodiment of the invention the macro mobilitymanagement is mobile IP-type mobility management. A typical feature ofthe mobility agent in the mobile IP is that it periodically transmitsagent advertisement messages to the mobile nodes in order to advertiseits services. The mobile nodes use these advertisements to determine thecurrent point of attachment to the Internet. In merit of the newconnection established by the access node to the preferred mobilityagent, the agent advertisement messages sent by the new mobility agentcan be received by the mobile node, and thereby the mobile node is ableto detect the change of the attachment point (i.e. mobility agent) andto initiate standard mobile IP registration.

[0021] Thus, an advantage of the invention is that the inventive newfunctionality in the access node also enables to detect the movement ofa mobile node on the macro mobility level, such as the mobile IP level,and to select and change the most optimal mobility entity in each partof the network, without needing any non-standard signalling or procedurein other elements of the access network or on the macro mobilitymanagement level.

[0022] In the packet access network a mobile station which the mobilenode is associated with may have two or more packet protocol (PDP)contexts open at the same time. The above described new connectionshould be established for any macro mobility related PDP context themobile station may have. However, all of the PDP contexts are notnecessarily related to the macro mobility management and thereforeshould not be involved in the change of the mobility entity. Thus, theremay be need for the access node to be able to distinguish the macromobility management dedicated PDP contexts from other active PDPcontexts of the mobile station. In an embodiment of the invention, theinformation transferred from the old access node to the new access nodeis provided with an information field which indicates the differenttypes of the PDP contexts, or at least the macro mobility managementrelated PDP contexts. This allows the PDP context types to bedistinguished, and therefore, also the macro mobility management relatedPDP context can be recognized and the mobility entity of the recognizedPDP contexts changed by the access node.

[0023] The route optimization saves the transmission resources in thepacket radio system, and possibly also makes the connection faster asthe connection leg between the access node and the mobility entity isshorter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following, the invention will be described in greaterdetail by means of preferred embodiments with reference to theaccompanying drawings, in which

[0025]FIG. 1 illustrates GPRS network architecture,

[0026]FIG. 2 is a signalling diagram illustrating the method accordingto the invention,

[0027]FIG. 3 is a flow diagram illustrating the function of the supportnode,

[0028]FIG. 4 is a signalling diagram illustrating the method accordingto the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0029] The present invention can be applied to any communicationsrequiring macro mobility management which overlays the mobilitymanagement of an access network. The invention suits especially well forsupporting mobile IP-type mobility management in an access network. Theaccess network may be any access network, such as a radio accessnetwork. The invention can be especially preferably used for providing ageneral packet radio service GPRS in the pan-European digital mobilecommunication system GSM (Global System for Mobile Communication) or incorresponding mobile communication systems, such as DCS1800 and PCS(Personal Communication System), or in third generation (3G) mobilesystems, such as UMTS, implementing a GPRS-type packet radio. In thefollowing, the preferred embodiments of the invention will be describedby means of a GPRS packet radio network formed by the GPRS service andthe 3G or GSM system without limiting the invention to this particularaccess system.

[0030] A GPRS architecture utilizing 3G radio access (such as UMTS) or2G radio access (such as GSM) is illustrated in FIG. 1. The GPRSinfrastructure comprises support nodes such as a GPRS gateway supportnode (GGSN) and a GPRS serving support node (SGSN). The main functionsof the GGSN nodes involve interaction with the external data network.The GGSN updates the location directory using routing informationsupplied by the SGSNs about an MS's path and routes the external datanetwork protocol packet encapsulated over the GPRS backbone to the SGSNcurrently serving the MS. It also decapsulates and forwards externaldata network packets to the appropriate data network and handles thebilling of data traffic.

[0031] The main functions of the SGSN are to detect new GPRS mobilestations in its service area, handle the process of registering the newMSs along with the GPRS registers, send/receive data packets to/from theGPRS MS, and keep a record of the location of the MSs inside of itsservice area. The subscription information is stored in a GPRS register(HLR) where the mapping between a mobile's identity (such as MS-ISDN orIMSI) and the PSPDN address are stored. The GPRS register acts as adatabase from which the SGSNs can ask whether a new MS in its area isallowed to join the GPRS network.

[0032] The GPRS gateway support nodes GGSN connect an operator's GPRSnetwork to external systems, such as other operators' GPRS systems, datanetworks 11, such as an IP network (Internet) or an X.25 network, andservice centres. Fixed hosts 14 can be connected to the data network 11e.g. by means of a local area network LAN and a router 15. A bordergateway BG provides access to an inter-operator GPRS backbone network12. The GGSN may also be connected directly to a private corporatenetwork or a host. The GGSN includes GPRS subscribers' PDP addresses androuting information, i.e. SGSN addresses. Routing information is usedfor tunnelling protocol data units PDU from the data network 11 to thecurrent switching point of the MS, i.e. to the serving SGSN. Thefunctionalities of the SGSN and GGSN can be connected to the samephysical node (SGSN+GGSN).

[0033] The home location register HLR of the GSM network contains GPRSsubscriber data and routing information, and it maps the subscriber'sIMSI into one or more pairs of the PDP type and PDP address. The HLRalso maps each PDP type and PDP address pair into a GGSN node. The SGSNhas a Gr interface to the HLR (a direct signalling connection or via aninternal backbone network 13). The HLR of a roaming MS and its servingSGSN may be in different mobile communication networks.

[0034] The intra-operator backbone network 13, which interconnects anoperator's SGSN and GGSN equipment, can be implemented, for example, bymeans of a local network, such as an IP network. It should be noted thatan operator's GPRS network can also be implemented without theintra-operator backbone network, e.g. by providing all features in onecomputer.

[0035] Network access is the means by which a user is connected to atelecommunication network in order to use the services and/or facilitiesof that network. An access protocol is a defined set of procedures thatenables the user to employ the services and/or facilities of thenetwork. The SGSN, which is at the same hierarchical level as the mobileswitching centre MSC, keeps track of the individual MSs' location andperforms security functions and access control. GPRS securityfunctionality is equivalent to the existing GSM security. The SGSNperforms authentication and cipher setting procedures based on the samealgorithms, keys, and criteria as in the existing GSM. The GPRS uses aciphering algorithm optimised for packet data transmission.

[0036] In order to access the GPRS services, an MS will first make itspresence known to the network by performing a GPRS attach. Thisoperation establishes a logical link between the MS and the SGSN, andmakes the MS available for the SMS over the GPRS, paging via the SGSN,and notification of incoming GPRS data. More particularly, when the MSattaches to the GPRS network, i.e. in a GPRS attach procedure, the SGSNcreates a mobility management context (MM context), and a logical linkLLC (Logical Link Control) is established between the MS and the SGSN ina protocol layer. MM contexts are stored in the SGSN and MS. The MMcontext of the SGSN may contain subscriber data, such as thesubscriber's IMSI, TLLI and location and routing information, etc.

[0037] In order to send and receive GPRS data, the MS will activate thepacket data address that it wants to use, by requesting a PDP activationprocedure. This operation makes the MS known in the corresponding GGSN,and interworking with external data networks can begin. Moreparticularly, one or more PDP contexts are created in the MS, GGSN andSGSN, and stored in the serving SGSN in connection with the MM context.The PDP context defines different data transmission parameters, such asthe PDP type (e.g. X.25 or IP), PDP address (e.g. IP address), qualityof service QoS and NSAPI (Network Service Access Point Identifier). TheMS activates the PDU context with a specific message, Activate PDPContext Request, in which it gives information on the TLLI, PDP type,PDP address, required QoS and NSAPI, and optionally the access pointname APN. The SGSN sends a create PDP context message to the GGSN whichcreates the PDP context and sends it to the SGSN. The SGSN sends the PDPcontext to the MS in a Activate PDP Context Response message, and avirtual connection or link between the MS and the GGSN is established.As a result, the SGSN forwards all the data packets from the MS to theGGSN, and the GGSN forwards to the SGSN all data packets received formthe external network and addressed to the MS. The PDP context is storedin the MS, SGSN and GGSN. When the MS roams to the area of a new SGSN,the new SGSN requests MM and PDP contexts from the old SGSN.

[0038]FIG. 1 illustrates the implementation of mobile IP in the GPRS/3Genvironment.

[0039] The MS can be a laptop computer PC connected to a packet radioenabled cellular telephone. Alternatively, the MS can be an integratedcombination of a small computer and a packet radio telephone, similar inappearance to the Nokia Communicator 9000 series. Yet furtherembodiments of the MS are various pagers, remote-controllers,surveillance and/or data-acquisition devices, etc. The user of a mobilestation MS subscribes to a special Mobile IP service. The subscriptioninformation is stored in the Home Location Register HLR together withthe user's home IP address.

[0040] In FIG. 1 the foreign agents FA are located in (integrated into)GGSNs. Alternatively, the SGSN and the GGSN are co-located, and the FAsare located in SGSN+GGSNs. It should be noted that there may be morethan one SGSN and GGSN in one network. All GGSNs may not have FAs. EachFA has an IP address in the Internet and in the operator's own privateGPRS/3G backbone network. More precisely, the FA's IP address is suchthat IP packets destined to that address are routed in the Internet tothe GGSN associated with the FA. When the MN leaves its home subnet andregisters to a new FA, it can no longer be reached on the basis of itshome IP address alone, but must be assigned an address belonging to thevisited network, called the care-of address (COA). The care-of addresspositively identifies the instantaneous location of the mobile terminaland may be: 1) the IP address of the FA belonging to the visitednetwork, or 2) an IP address acquired directly by the mobile terminalthrough an autoconfiguration mechanism from the local IP address space,in which case the term co-located care-of address is used. Whenregistering to a new FA and obtaining a COA, the MN which registers witha home agent HA in its home network informs the latter of its COA. InFIG. 1 a home agent HA is located in a data network 11 which is the homenetwork of the mobile node MN associated with the mobile station MS. Asecond host 14 wishing to communicate with the MN need not be aware ofthe fact that the MN has moved: it simply sends IP packets addressed toMN's home IP address. These packets are routed via normal IP routing tothe MN's home network, there they are intercepted by the HA. The HAencapsulates each such packet in another IP packet which contains theMN's COA as these packets are thus delivered to the FA (a process calledtunnelling). The FA forwards the IP packet to the GGSN. The GGSNforwards the IP packet (which may be encapsulated for transmission overthe GPRS backbone) to the serving SGSN which further forwards the IPpacket to the MS/MN. Packets from the MN to the other host 14 need notnecessarily be tunneled: the MN may simply send them to the GGSN whichdirectly forwards the packets to the second host 14, withoutinterception by the FA or the HA.

[0041] As noted above, according to the present invention the SGSNdetermines whether it is preferable to change the mobility agent of theIP session or not. A preferred embodiment of the invention will be nowdescribed with reference to FIGS. 1, 2, 3 and 4.

[0042] A reference is now made to FIG. 1. The home network of the mobilestation MS is the GPRS/3G network 1. The user of the mobile station MSsubscribes to a special mobile IP service, and an IP application in theMS or in a separate data terminal is a mobile node MN in a mobile IPcommunication. It is assumed that the MS/MN is attached to the homenetwork 1 and the radio access network RAN1 (PS1 and PSC/RNC1). Aserving support node in the home network is SGSN1. MM and PDP contextshave been created for the mobile IP service as described above, and avirtual connection is provided between the MS/MN and the SGSN1 as wellas between the SGSN1 and a gateway node GGSN1 which has an associatedforeign agent FA1. Thus, the IP packets addressed to the MN can beforwarded to the MN over the home network 1 and RAN1. The COA of the MNhas been registered to the home agent HA in the home network 11 of theMN, so that mobile IP tunnelling is provided from the HA to theGGSN/FA1.

[0043] Let us now assume that the MS/MN moves to the service area ofanother GPRS/3G network 2 which is served by support node SGSN2. Whenthe MS/MN arrives at a new RAN2, the MS part listens to radio broadcastmessages, which contain information about radio parameters, network andcell identity, etc. as well as information about available core network,service providers, service capabilities etc. On the basis of thebroadcast the MS determines that the network and/or the routing area haschanged. Upon detecting a change of routing area, the MS/MN sends arouting area update request to the new SGSN, namely SGSN2, as shown inFIG. 2. The new SGSN2 sends a SGSN context request message to the oldSGSN1 (in step 2) to obtain the MN and PDP contexts for the MS/MN. Theold SGSN1 responds with a SGSN context response message which containsthe MN and PDP contexts (step 3). According to the preferred embodimentof the invention, the information transferred from the old access nodeto the access node may be provided with an information field whichindicates the different types of the PDP contexts, or at least theMobile IP related PDP contexts. This allows the SGSN to distinguish theMobile IP dedicated PDP contexts from other active PDP contexts of themobile station which should not be involved in the change of themobility agent. There are various possible ways to implement the PDPcontext type information. For example, a PDP Context InformationElement, which is carried in the SGSN Context Response message in theGPRS (and in the forward SNRC relocation message in the UMTS) may beprovided with a field indicating the type of service used over the PDPcontext. The type field may contain an access Point Name which has avalue indicating a Mobile IP PDP context. Spare bits in the PDP ContextInformation Element may be used for the new field, or alternatively thenew field may be an extension of the current PDP Context InformationElement format. It should be noted, however, that the exactimplementation is not relevant to the invention. It is only relevant, inthis specific embodiment, that the information received from the oldSGSN enables the new SGSN to determine which one(s) of the PDP contextsis (are) dedicated to the Mobile IP.

[0044] In step 4 the new SGSN2 may, in certain situations, executeauthentication/security functions which may involve an interrogation tothe HLR of the MS/MN. If the user has at least one activated PDPcontext, the new SGSN2 sends a SGSN context acknowledge message to theold SGSN1. The old SGSN1 may now start forwarding of buffered datapackets belonging to the activated PDP context, if any, to the newSGSN2. The new SGSN2 will now execute the foreign agent check procedureaccording to the present invention, step 6, if there is at least one PDPcontext for the Mobile IP. The FA check procedure according to thepreferred embodiment of the present invention is illustrated in FIG. 3.In step 31 the new SGSN2 checks whether there is a preferred FA definedfor it. For example, the SGSN2 may check whether there is an address ofa preferred FA2 stored in the SGSN2. In this example, the address of theGGSN/FA2 is found, and the procedure proceeds to step 32. In step 32 thenew SGSN2 checks whether the address of the old FA1 obtained in the PDPcontext from the old SGSN1 is the same as the stored address of thepreferred FA2. In this example, the old FA1 is in the GGSN1 and thepreferred FA2 of the SGSN2 is in the GGSN2, and the addresses do notmatch. The procedure proceeds to the step 33 in which the new SGSN2deletes the PDP context in the old GGSN/FA1 by sending a delete PDPcontext requests to the old GGSN/FA1, as shown in FIG. 2. As a result,any active PDP context in the GGSN/FA1 is deactivated, and the GGSN/FA1acknowledges by sending a delete PDP context response to the new SGSN2(step 8 in FIG. 2). Referring again to FIG. 3, the process proceeds tostep 34 wherein the new SGSN2 creates a PDP context in the preferredGGSN/FA2 by sending a create PDP context requests to the new GGSN/FA2(step 9 in FIG. 2). The GGSN/FA2 creates the PDP context for the MS/MNand returns a create PDP context response to the new SGSN2 (step 10 inFIG. 2). The new SGSN2 establishes MN and PDP contexts for the MS/MN,and responds to the MS/MN with routing area update accept message (step11). The MS/MN acknowledges with a routing area update complete message(step 12). A virtual connection has thus been established between theMS/MN and the GGSN/FA2.

[0045] All the previous procedures have been executed in the GPRS/3Glayer only. The overlaying mobile IP layer and thereby the MN part ofthe MS/MN are not aware of the change of the FA. However, due to thenewly established connection to the GGSN/FA2 the MN is able to hear theagent advertisement messages broadcast by the new FA2 in accordance withthe mobile IP protocol. Upon receiving the agent advertisement from thenew FA2, the MN is able to detect a change in the point of attachment,i.e. change of FA, in accordance with the MIP standard. The agentadvertisement message may also include the care-of-address COA, or theMN may acquire the COA in accordance with the MIP standard. Then themobile node MN registers its COA with its home agent HA in accordancewith the MIP standard (step 14 in FIG. 2). Depending on its method ofattachment, the MN will register either directly with its HA, or throughthe new FA which forwards the registration to the HA. Thereafter, themobile IP tunnelling between the HA and the old GGSN/FA1 is released andnew mobile IP tunnelling is established between the HA and the newGGSN/FA2, in accordance with the mobile procedures (step 15 in FIG. 2).

[0046] As a result, the change of FA has been detected and establishedusing standard GPRS/3G procedures and messages and standard mobile IPprocedures and messages everywhere else but in the SGSN2. Also in theSGSN2 only minor modifications are needed. Firstly, a preferred FA hasto be defined for the SGSN2. Secondly, the need for an FA change needsto be executed. Thirdly, the new SGSN is arranged to automatically andindependently (without involvement of the MS) delete the PDP context inthe old GGSN and to create a new PDP context in the new GGSN.

[0047] Referring again to FIG. 3, if no preferred FA is defined for theSGSN1 in step 31, or the old FA is the same as the preferred FA (theaddresses match) in step 32, the process proceeds to step 35. In step 35the new SGSN1 updates the PDP context in the old GGSN/FA1, as shown instep 41 in FIG. 4. The old GGSN/FA1 updates the PDP context to containthe address of the new SGSN2, and sends an update PDP context responseto the new SGSN2 in step 42. Then the new SGSN2 sends the RA updateaccept message to the MS/MN (step 43) and the MS/MN responds with the RAupdate complete message (step 44). A virtual connection is thusestablished between the MS/MN and the old GGSN/FA via the new SGSN1. Asthe FA and the COA are unchanged, no registration to the HA is needed.In FIG. 4 steps 1 to 6 are similar to those in FIG. 2.

[0048] The description only illustrates preferred embodiments of theinvention. The invention is not, however, limited to these examples, butit may vary within the scope and spirit of the appended claims.

1. A method of providing macro mobility management for a mobile node inan access system comprising a plurality of mobile nodes, a first and asecond access node serving said mobile nodes within the first and secondparts of the access system, respectively, at least one first gatewaynode for interfacing said first part of the access system with externalnetworks , and a first mobility entity which is associated with said atleast one first gateway node and arranged to provide macro mobilitymanagement routing services to the mobile nodes while registered to thefirst part of the access system, said method comprising steps ofestablishing a session between one of said plurality of mobile nodes anda second party via said first access node (SGSN1) and said firstmobility entity, checking whether there is a second mobility entitywhich is more preferred in respect of routing than said first mobilityentity and reacting to said checking by A) maintaining a connection tosaid first mobility entity if there is no second mobility entity whichis more preferred than said first one, and B) opening new connection tosaid second mobility entity if said more preferred second mobilityentity is available, and initiating macro mobility managementregistration.
 2. The method according to claim 1, comprising reroutingthe session via said second access node in response to a movement ofsaid one of mobile nodes to said second part of the system.
 3. Themethod according to claim 1, comprising closing the connection to saidfirst mobility entity when said more preferred second mobility entity isavailable.
 4. The method according to claim 1, wherein said macromobility management is Internet Protocol-type, or IP-type mobilitymanagement, and wherein an agent advertisement message is sent from saidsecond mobility entity to said one mobile node over said new connection,said agent advertising message enabling said one mobile node to detect achange of attachment point and to initiate mobile IP registration. 5.The method according to claim 1, comprising storing in said secondaccess node the identity of said preferred mobility entity of saidsecond access node, checking in said second access node, in response toa movement of said one mobile node from said first access node to saidsecond access node, whether the identity of said first mobility entityand said stored identity of said preferred mobility entity match or not,maintaining a connection to said first mobility entity if the identitiesmatch, and closing the connection to said first mobility entity andopening a new connection to said preferred mobility entity if saididentities do not match.
 6. The method according to claim 1 or 2 in aradio access system, wherein said steps of closing and opening of theconnection comprise steps of closing and opening of a packet protocolcontext.
 7. The method according to claim 6, comprising transferring thepacket protocol contexts of a mobile station which the mobile node isassociated with from the first access node to the second access node,along with information which indicates which one or ones of the packetradio protocol contexts relate to the macro mobility management,distinguishing the macro mobility management related packet protocolcontext(s) from possible other packet protocol contexts on the basis ofsaid information at the second access node, performing said steps ofopening and closing solely on the macro mobility management relatedpacket protocol context(s).
 8. The method according to claim 1, whereinsaid preferred mobility entity of said second access node is a foreignagent associated with a gateway node in said second part of the accessnetwork.
 9. The method according to claim 1, wherein said identityincludes the address of the mobility entity.
 10. An access system,comprising a plurality of mobile nodes, a first nd a second access nodeserving said mobile nodes within the first and second parts of theaccess system, respectively, at least one first gateway node forinterfacing said first part of the access system with external networks,a first mobility entity which is associated with said at least one firstgateway node and arranged to route a connection to any one of saidmobile nodes while said mobile node is registered to the first part ofthe access system, a mechanism which checks whether there is a secondmobility entity which is more preferred in respect of routing than saidfirst mobility entity, a mechanism which opens a new connection to saidsecond mobility entity if said more preferred second mobility entity isavailable according to said checking, said mobile node being arranged todetect a change of attachment by means of said new connection and toinitiate macro mobility management registration.
 11. The systemaccording to claim 10, comprising a rerouting mechanism by which saidconnection initially routed via said first access node and said firstmobility entity can be routed via said second access node in response toa movement of said one of mobile nodes to said second part of the accesssystem.
 12. The system according to claim 10, comprising a mechanismwhich closes a connection to said first mobility entity when said morepreferred second mobility entity is available according to saidchecking.
 13. The system according to claim 10, comprising said macromobility management being Internet Protocol-type, or IP-type, mobilitymanagement, said second mobility entity being arranged to send an entityadvertisement message to said one mobile node over said new connection,said mobile node being arranged to detect a change of attachment bymeans of said entity advertising message and to initiate mobile IPregistration.
 14. The system according to claim 10, wherein saidpreferred mobility entity of said second access node is a foreign agentassociated with a gateway node in said second part of the accessnetwork.
 15. The system according to claim 10, wherein said secondaccess node is arranged to make said checking.
 16. The system accordingto claim 15, wherein the second access node is arranged to store theidentity, such as address, of the preferred foreign agent for thechecking purposes.
 17. The system according to claim 10 or 11,characterized in that said closing and opening of the connectioncomprise closing a packet protocol context in the gateway node of thefirst mobility entity and opening a packet protocol context in thegateway node of the preferred mobility entity .
 18. The system accordingto claim 17, wherein said maintaining of the connection comprisesupdating of a packet protocol context of the mobile node (in the gatewaynode of the first mobility entity.
 19. The system according to claim 17,wherein packet protocol contexts of a mobile station which the mobilenode is associated with are associated with information which indicateswhich one or ones of the packet protocol contexts relate to the macromobility management, and wherein the access node is arranged todistinguish the macro mobility management related packet protocolcontext(s) from possible other packet protocol contexts on the basis ofsaid information and to said steps of opening and closing solely on themacro mobility management related packet protocol context(s).
 20. Thesystem according to claim 19, wherein said information is provided in amessage transferring the packet protocol context(s) from said otheraccess node to said access node.
 21. An access node for an access systemcomprising a plurality of mobile nodes, access nodes serving said mobilenodes within respective parts of the access system, at least two gatewaynodes for interfacing the access system with external networks (11), andat least two mobility entities which are associated with different onesof said at least two gateway nodes and arranged to provide macromobility management routing services to the mobile nodes whileregistered to the access system, said access node comprising means forchecking, when a mobile node having a connection through another accessnode and a first mobility entity is accessing the system via said accessnode, whether there is another mobility entity which is more preferredin respect of routing than said first mobility entity, means responsiveto said checking means for opening a new connection to said preferredother mobility entity if said more preferred other mobility entity isavailable.
 22. The access node according to claim 21, comprising meansfor closing a connection to said first mobility entity when said morepreferred other mobility entity is available.
 23. The access nodeaccording to claim 21, wherein said checking means comprises means forstoring the identity, such as address, of said preferred other mobilityentity of said access node . means for checking, in response to amovement of said mobile node (MS/MN) from said other access node to saidaccess node whether the identity of said first mobility entity and saidstored identity of said preferred mobility entity match or not.
 24. Theaccess node according to claim 22 , wherein said closing and openingmeans comprise means for maintaining a connection to said first mobilityentity if the identities match, and means for closing the connection tosaid first mobility entity and opening new connection to said preferredmobility entity if said identities do not match.
 25. The access nodeaccording to any one of claims 22, 23 or 24 , wherein said access systemis a radio access system, and wherein said means for closing and openingof the connection comprise means for closing a packet protocol contextin the gateway node of the first mobility entity and opening a packetprotocol context in the gateway node of the preferred mobility entity.26. The access node according to claim 25, wherein said means formaintaining the connection comprise means for updating a packet protocolcontext of the mobile node in the gateway node of the first mobilityentity.
 27. The access node according to claim 25, wherein packetprotocol contexts of a mobile station which the mobile node isassociated with are associated with information which indicates whichone or ones of the packet protocol contexts relate to the macro mobilitymanagement, and wherein the access node is arranged to distinguish themacro mobility management related packet protocol context(s) frompossible other packet protocol contexts based on said information and toperform said steps of opening and closing solely on the macro mobilitymanagement related packet protocol context(s).
 28. The access nodeaccording to claim 27, wherein said information is provided in a messagetransferring the packet protocol context(s) from said other access nodeto said access node.
 29. The access node according to any one of claims21 to 28, wherein said macro mobility management is InternetProtocol-type, or IP-type, mobility management.